1. Field of the Invention
The invention generally relates to synchronization of media streams.
2. Background
Multiple media streams can be combined to provide combined media (e.g., multimedia) content for consumption by a user. It is desirable for such media streams to be synchronized in order to provide the intended combined media experience for the user. However, synchronization in some environments, such as an asynchronous networked environment, poses challenges. For example, in an internet protocol (IP) networked environment, a sending device traditionally includes timing information in each packet (i.e., encapsulated portion) of a media stream so that a receiving device may organize the packets in a designated order and play back the packets at a designated rate, as specified by the timing information. The timing information from the packets of each media stream is correlated and applied to the combined media content before the content is played back or presented to the user.
Correlation of timing information across media streams requires that such timing information be of the same time origin. Such time origin traditionally is a network time server in a network. For instance, IP endpoints of an IP network typically retrieve time information from the network time server using a protocol such as Network Time Protocol (NTP). However, the retrieved timing information often has accuracy in the order of hundreds of milliseconds (˜200 ms) due to network latency and other factors. As a result, the timestamp values that are applied to the media stream packets inherit a few hundred milliseconds of time uncertainties.
Due to the inherit time uncertainty regarding each stream over the network, the overall uncertainty increases as the number of streams increases. This uncertainty has a direct effect on the accuracy of cross correlation that is needed for the synchronization of the combined media content and therefore the impact on the combined media experience of the user.